1. Field of the Invention.
This invention relates to a method of controlling color and density correction values in portraiture printer control systems.
2. Description of the Prior Art
Film negatives have been analyzed to determine proper color and density corrections in the photographic field for at least thirty years. At first, the analysis was based upon large area transmission density of red, green and blue, sometimes referred to as "LATD" measurements. The idea was that the overall color content of any given print should integrate to gray. Based upon the LATD measurements, the red, green and blue exposure times would be adjusted so that the overall integrated color of the print was gray.
By the 1960's, it was recognized that integration to gray did not completely handle all possible situations. Certain types of photographs would not print properly with integration-to-gray. These were typically referred to as "color failure" and "density failure" negatives. An example of a failure negative is a child in a red snowsuit standing in front of a snow bank. That type of scene does not have equal amounts of red, green and blue. In addition, the subject in the center of the photograph is abnormally dark compared to the background. If integration-to-gray were used solely to control exposure time, the child's face would be off-color and may be either abnormally dark or abnormally light. Other examples of failure negatives include beach and snow scenes, photographs taken using flash photography, and photographs taken under artificial lighting.
During the 1970's and into the early 1980's, a number of companies (most notably Kodak, Gretag, Agfa, Pako and Fuji Photo) developed automatic color and density analysis equipment which controlled photographic printers. For example, Terashita U.S. Pat. No. 4,641,959 discloses an automatic color printing control system. In general, these systems divided each negative into areas or pixels and performed some form of computer analysis on those pixels to determine the proper density and color corrections.
The Terashita patent also discusses the desirability of locating regions of flesh tones. Terashita discloses a method of detecting a principal subject for determining printing exposures. An individual visually inspects each negative and determines a region containing the principal subject. If the region contains flesh tones, printer exposure times are adjusted to create prints having more accurate flesh tones. In this method, however, the individual is relatively inefficient and prone to errors. The method used in the Terashita patent and the other color and density analysis techniques developed in the 1970's and early 1980's dealt with amateur photography, where the range of subjects and scenes which could be photographed was virtually unlimited. Thus, the negative analysis which was performed had to be very generalized.
In portrait photography, the range of subjects and scenes is much more limited than in amateur photography. In addition, the most important part of portrait photography is obtaining prints having proper flesh tones.
Hopson U.S. Pat. No. 4,422,745 entitled "Camera System" discloses a method of controlling the printing process for portraits. The camera system is used to take portraits of a large number of individuals such as students for school pictures. The camera system records bar code information on the exposed film alongside each image. That bar code information relates, for instance, to order information, student number and the like. This information can be used to control the number and size of prints produced. The student number is written alongside the print to aid in distribution.
Although the Hopson patent substantially reduces the labor required of a photographer to record information relating to orders and student numbers, it does not simplify the method of locating the principal subject in each portrait for determining printing parameters needed for obtaining prints having correct flesh tones.
The prior art of portrait photography lacks a simple method of automatically controlling a photographic printer to produce prints having proper flesh tones in their principal subjects.